1. Field of the Invention
The present invention relates to the field of manufacture of liquid crystal displays, and in particular to a method and a device for coating an alignment film.
2. The Related Arts
Liquid crystal displays (LCDs) have a variety of advantages, such as thin device body, low power consumption, and being free of radiation, and are thus widely used. However, it is well known that the liquid crystal displays are passive light emission devices and the liquid crystal material does not give off light by itself. Thus, most of the liquid crystal displays that are currently available in the market are backlighting liquid crystal displays, which comprise a liquid crystal display panel and a backlight module.
The operation principle of the liquid crystal display panel is that, with liquid crystal molecules interposed between two parallel glass substrates, a driving voltage is applied to the two glass substrates to control the liquid crystal molecules to change direction in order to refract out light emitting from the backlight module to generate an image. The liquid crystal display panel is generally made up of a color filter (CF) substrate, a thin-film transistor (TFT) array substrate, liquid crystal (LC) interposed between the CF substrate and the TFT array substrate, and a sealant and the manufacturing process generally comprises: a front stage of array process (including thin film, yellow light, etching, and film stripping), an intermediate stage of cell process (including laminating the TFT substrate and the CF substrate), and a rear stage of assembling process (including mounting of drive ICs and printed circuit board), in which the front stage of array process is generally to form the TFT substrate in order to control the movement of the liquid crystal molecules; the intermediate stage of cell process is generally to fill the liquid crystal between the TFT array substrate and the CF substrate and to seal the liquid crystal between the TFT array substrate and the CF substrate; and the rear stage of assembling process is generally to mount the drive ICs and to integrate the printed circuit board in order to achieve driving of the liquid crystal molecules to rotate for displaying images.
Heretofore, in the intermediate stage of cell process, an alignment film (polyimide, PI) is first formed on the TFT array substrate and the CF substrate. Then, a sealant for an enclosing frame is coated on the TFT array substrate and, thereafter, liquid crystal is dropped therein. Afterward, the TFT array substrate and the CF substrate are laminated in a vacuum condition. Finally, ultraviolet light is applied to irradiate and cure the enclosing frame sealant so as to complete the packaging of the TFT array substrate and the CF substrate.
As shown in FIG. 1, techniques that are conventionally used to coat an alignment film often adopt inkjet techniques, of which a practical operation process is as follows: Alignment liquid is first deposited in a pressurization tank 100 and then, the alignment liquid is fed to a supply tank 200 by a liquid pump 300 connected between the pressurization tank 100 and the supply tank 200 to have the alignment liquid contained in the supply tank 200 subsequently conveyed through a supply conduit 400 to an alignment liquid jet nozzle 500. Finally, the alignment liquid jet nozzle 500 applies the alignment liquid to a substrate 700 that is placed on a work tale 600 that is reciprocally movable frontward and rearward, and leftward and rightward, so as to achieve coating of an alignment film.
However, the primary ingredients of the alignment liquid include polyimide, N-methylpyrrolidone (NMP), and ethylene glycol monobutyl ether (BC), having a relatively high viscosity. For such an alignment liquid having a high viscosity, the known inkjet techniques cannot effectively jet it so that it is not possible to ensure surface uniformity of an alignment film.